linux-kernel - Re: [PATCH v4 07/10] tools/nolibc: clean up mmap() support

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Message-Id: <20230622190843.1189684-1-falcon@tinylab.org>
Date:   Fri, 23 Jun 2023 03:08:43 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     thomas@...ch.de
Cc:     arnd@...db.de, david.laight@...lab.com, falcon@...ylab.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-riscv@...ts.infradead.org, w@....eu
Subject: Re: [PATCH v4 07/10] tools/nolibc: clean up mmap() support

Hi, Thomas

> On 2023-06-19 23:51:20+0800, Zhangjin Wu wrote:
> > Do several cleanups together:
> > 
> > - Since all supported architectures have my_syscall6() now, remove the
> >   #ifdef check.
> > 
> > - Move the mmap() related macros to tools/include/nolibc/types.h
> > 
> > - Apply the new __sysret() to convert the calling of sys_map() to
> >   oneline code
> > 
> > Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
> > ---
> >  tools/include/nolibc/sys.h   | 24 +-----------------------
> >  tools/include/nolibc/types.h | 11 +++++++++++
> >  2 files changed, 12 insertions(+), 23 deletions(-)
> > 
> > diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> > index 8a6e16472d54..1c02cec3bcd9 100644
> > --- a/tools/include/nolibc/sys.h
> > +++ b/tools/include/nolibc/sys.h
> > @@ -624,26 +624,11 @@ int mknod(const char *path, mode_t mode, dev_t dev)
> >  	return __sysret(sys_mknod(path, mode, dev));
> >  }
> >  
> > -#ifndef MAP_SHARED
> > -#define MAP_SHARED		0x01	/* Share changes */
> > -#define MAP_PRIVATE		0x02	/* Changes are private */
> > -#define MAP_SHARED_VALIDATE	0x03	/* share + validate extension flags */
> > -#endif
> > -
> > -#ifndef MAP_FAILED
> > -#define MAP_FAILED ((void *)-1)
> > -#endif
> > -
> >  #ifndef sys_mmap
> >  static __attribute__((unused))
> >  void *sys_mmap(void *addr, size_t length, int prot, int flags, int fd,
> >  	       off_t offset)
> 
> This could return a plain integer type instead to save some casts.
> Not sure if API compatibility is guaranteed for the raw sys_ functions.
>

Seems musl simply not provide the sys_xxx() functions, but let the library
routines call __syscall() directly. If we can treat these sys_xxx() as internal
functions, perhaps we can simply let the return type of sys_xxx() as 'long' to.

    $ grep "^void \*sys_" -ur tools/include/nolibc/sys.h 
    void *sys_brk(void *addr)
    void *sys_mmap(void *addr, size_t length, int prot, int flags, int fd,

Thanks,
Zhangjin


> >  {
> > -#ifndef my_syscall6
> > -	/* Function not implemented. */
> > -	return (void *)-ENOSYS;
> > -#else
> > -
> >  	int n;
> >  
> >  #if defined(__NR_mmap2)
> > @@ -654,20 +639,13 @@ void *sys_mmap(void *addr, size_t length, int prot, int flags, int fd,
> >  #endif
> >  
> >  	return (void *)my_syscall6(n, addr, length, prot, flags, fd, offset);
> > -#endif
> >  }
> >  #endif
> >  
> >  static __attribute__((unused))
> >  void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset)
> >  {
> > -	void *ret = sys_mmap(addr, length, prot, flags, fd, offset);
> > -
> > -	if ((unsigned long)ret >= -4095UL) {
> > -		SET_ERRNO(-(long)ret);
> > -		ret = MAP_FAILED;
> > -	}
> > -	return ret;
> > +	return (void *)__sysret((unsigned long)sys_mmap(addr, length, prot, flags, fd, offset));
> >  }
> >  
> >  static __attribute__((unused))
> > diff --git a/tools/include/nolibc/types.h b/tools/include/nolibc/types.h
> > index f96e28bff4ba..f889d4e0ac7e 100644
> > --- a/tools/include/nolibc/types.h
> > +++ b/tools/include/nolibc/types.h
> > @@ -81,6 +81,17 @@
> >  #define MAXPATHLEN     (PATH_MAX)
> >  #endif
> >  
> > +/* flags for mmap */
> > +#ifndef MAP_SHARED
> > +#define MAP_SHARED		0x01	/* Share changes */
> > +#define MAP_PRIVATE		0x02	/* Changes are private */
> > +#define MAP_SHARED_VALIDATE	0x03	/* share + validate extension flags */
> > +#endif
> > +
> > +#ifndef MAP_FAILED
> > +#define MAP_FAILED ((void *)-1)
> > +#endif
> > +
> >  /* whence values for lseek() */
> >  #define SEEK_SET       0
> >  #define SEEK_CUR       1
> > -- 
> > 2.25.1
> >